The invention concerns a device for improving the alignment accuracy in the case of a sheet-like material which, before further processing is aligned in a conveying plane positionally precisely with respect to its twisted position and its oblique position with respect to the machine direction.
U.S. Pat. No. 5,322,273, issued Jun. 21, 1994 in the name of Rapkin, et al., is directed to a sheet aligning device. This device for aligning a sheet moving along an essentially plane conveying path makes possible the alignment of a moving sheet in a number of orthogonal directions, for example transverse to the conveying path and in the direction of the conveying path, and for eliminating inclined positions.
The device has a first roller arrangement with a first backup roller, which is mounted so that it can turn around an axis, which lies in a plane extending parallel to the plane of the conveying path, and passes essentially at a right angle to the direction of sheet transport along the conveying path. A second roller arrangement has a second backup roller, which is mounted so that it can turn around an axis which lies in a plane extending parallel to the plane of the conveying path and passes essentially at a right angle to the direction of the sheet transport along the transport path. A third roller arrangement is provided which has a third backup roller, which is mounted so that it can turn around an axis, which lies in a plane extending parallel to the plane of the conveying path, and essentially at a right angle to the direction of the sheet transport along the conveying path. A third roller arrangement, which is capable of turning around an axis which lies in a plane extending parallel to the direction of sheet transport, is movable along its rotational axis in a direction passing transverse to the conveying path.
Finally, a control device is provided which is in an operating connection with the first, respectively second, respectively third arrangement, and optionally controls the rotation of the first and second roller arrangement, in order to align the leading edge of a sheet moving in a position located at a right angle to the direction of sheet transport along the conveying path. Further, the control direction controls the rotation and transverse motion of the third roller arrangement, in order to align the sheet moving in the direction passing transverse to the direction of the sheet transport as well as the direction in which the sheet moves along the conveying path.
The sheet alignment device known from U.S. Pat. No. 5,322,273 made it possible to satisfy the required alignment accuracy only to a limited degree. In order to achieve the required alignment accuracy, a comprehensive modification to the currently known sheet alignment device is necessary, which does not appear to be economical.
In the case of sheet-processing printing presses functioning according to the offset principle, the sheets are conveyed to the feed table in a overlapping arrangement, before they are aligned to side and pull guides provided in the level of the feed table. After successful alignment of the sheet-like material the latter is transferred to a preliminary gripper in the aligned condition, which accelerates the sheet-like material to machine speed and transfers it to a curved cylinder placed after the preliminary gripping device. Other alignment concepts for the most part use a cylindrical roller which has a rubber coating applied to the roller core. If an alignment of sheet-like material during the advance thereof is made by changing the speed between a left and right roller gripping the sheet-like material with such a configuration, the sheet-like material experiences a rotation around a turning point, which is located on the stationary roller, or during the advance is located outside the roller with the lower speed or between the two rollers. The actual point of contact between the sheet-like material and the roller is not defined; it is known only that it is located within the roller width. This uncertainty has an effect on the quality of the alignment result.
The object of the invention is to considerably improve the alignment accuracy of sheet-like material during the advance thereof in the direction of sheet travel.
According to the invention this object is achieved by the features of Patent claim 1.
The advantages attainable with the solution according to the invention are to be seen above all in the fact that the smallest possible contact surface is created between upper side of the sheet-like material to be aligned and the contact surface of the alignment element because of the geometrical shape of roller core surfaces, respectively elastic coatings applied thereto, such as, for example, rubber coatings. Thus the point of contact between printing material and roller is known or at least defined essentially more accurately as compared with the solutions known from the prior art, so that the quality of the alignment can be improved considerably. The more dimensionally stable the elastic material used for alignment can be made, the smaller the contact surface, which in each case is in contact with the surface of the sheet-like material, can be made.
In an advantageous embodiment of the concept underlying the invention, the aligning elements can be made as rollers, that is, as rotation-symmetrical bodies, which include a roller core as well as a ring-shaped coating material applied thereto. Thus, for example, the roller core can be made out of an inexpensive material, compared with the ring-shaped coating material applied thereto, further in this way it is possible to make the roller core more easily and the shape of the ring-shaped coating specifically.
In one embodiment, the ring-shaped coating on the peripheral surface of the roller core can be applied as a liquid under pressure. In this embodiment the ring surface can be made, for example as an endless ring, which can be secured simply on the peripheral surface of the roller core. The coating also can be glued or cast onto the surface of the roller.
In a second embodiment, the ring-shaped coating on the peripheral surface of the roller core can be applied positively, for example with a shrink fit, to lock to the roller core. Preferably the annularly configured coating is made in one piece, so that no interruptions, but a continuous surface, can be made on the circumference of the roller core. The annular coating can be provided, for example, with a trapezoidal cross-section, which is distinguished in particular by a narrow and sharp-edged contact area between gently tapering edges for the upper side of the sheet-like material. The more point-like, the contact can be made, the more exactly can alignment results be achieved with the solution according to the invention.
If ring-like coatings are applied to the peripheral surfaces of the roller core, recesses for holding of these support elements can be included in the surfaces of the roller cores. The contact elements aligning the sheet-like material can be made in the surfaces of the roller cores as annular longitudinal grooves, thus ensuring support of the support elements to be introduced into this recess on the lateral surfaces thereof.
In order to eliminate the danger of damage to the contact areas between sheet-like material and the alignment elements, the latter are configured as narrow rings or as trapezoidal surfaces, and can be made as an elastic flexible material.
In a preferred use of the solution proposed according to the invention, in order to improve the alignment accuracy the latter can be placed in an aligning unit which can be located in front of a press, for example a sheet-processing printing press. The solution according to the invention can be used in aligning units which also can be used on digitally operating rotary printing presses, since the printing material processed there, be it films, cardboard, paper, or the like, also needs alignment before it is printed or, in a given case, processed in a digitally operating machine.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.